This invention pertains to printing equipment, particularly easy-to-use compact printing equipment.
Previously, offset presses have generally had plate cylinders, blanket cylinders and impression cylinders. In the case of multiple color printing, units consisting of these three cylinders are generally used in tandem, one three-cylinder unit for each color. The printed material is passed through one unit to the next until all the colors have been printed. The aforementioned plate cylinder consists of a clamp that affixes the plate to the cylinder's surface. The blanket cylinder is a cylinder around which the blanket is wrapped and, like the aforementioned plate drum, has a depression to accommodate the clamp in its outer periphery. Normally the aforementioned plate cylinder and blanket cylinder have an effective circumference greater than the length of one plate, and transfer and print one plate per revolution. There are, however, also some plate cylinders and blanket cylinders with effective circumferences the length of two plates. This is achieved by doubling the diameters of the plate and blanket cylinders and allows two types of plates to be printed per revolution.
Previously there have been offset presses of all sizes, from large offset sheet-feed rotary presses and web-fed offset rotary presses to small offset presses that handle B4 and A4 sheets. However, the fundamental necessity that offset presses have effective plate cylinder and blanket cylinder circumferences at least equal to the length of the plates has imposed a limit on the degree to which they can be miniaturized. Even compact B4 size offset presses have cylinders 20 cm or more in height. Another difficulty is that because both the plate cylinder and blanket cylinder are cylindrical, the dampening unit, inking unit, cleaning unit and drying unit must all be concentrated into a small area. This entails complex mechanical design and usually increases the difficulty of operation. In particular, in the case of small offset presses, because of the need to place the dampening and inking units next to the plate cylinder, concentrated into a small area around the plate cylinder, it is quite difficult to include the etching unit next the plate cylinder as well. Accordingly, with small presses the etching unit is usually a separate device.
Offset presses have had the advantage of relatively greater speed, simplicity and economy--and this accounts for their popularity--but they have also suffered from some disadvantages, such as the fine adjustment of dampening water and ink and rapid exchanges of the three cylinders, which necessitate complex mechanisms and a high level of operator skill. The combined large size and high level of operator skill. The combined large size and high prices of presses have tended to limit their use to firms that specialize in printing. Compact, inexpensive and easy-to-use presses suitable for the needs of general office printing (i.e., diverse, small-lot printing) have yet to be introduced.
In addition, printing ink dries quickly and thus can harden on the surface of the ink roller(s) if left uncleaned after printing, so detachment and cleaning of the ink roller unit is necessary after each print run. This dirty work before and after printing makes the printer difficult to use. Easy-to-use offset printer that can handle everything, including this particular operation, have yet to be introduced and are in demand.